1. Field of the Invention
The present invention relates to a cooking apparatus which uses a pyroelectric vapor sensor for performing control by detecting the state of vapor generated from food as the food is heated.
2. Description of the Prior Art
Sensing means used in conventional heating-cooking apparatuses are described below with reference to the drawings.
FIG. 1 shows a conventional high-frequency heating apparatus using a humidity sensor. As food is heated and the moisture contained therein boils off, the change of the humidity level in the heating apparatus suddenly changes from decrease to increase. With a humidity sensor, it is possible to determine the completion of cooking by detecting this point of change. Hence, in FIG. 1, the heating apparatus is controlled by detecting the resistance change in a humidity sensor 1 at which, along with a resistor 3, the voltage from a reference voltage supply 2 is divided. (An example such as disclosed in Japanese Laid-Open Patent Publication No. 53-77365)
There is also available a means, as shown in FIGS. 2 and 3, which uses a pyroelectric vapor sensor instead of a humidity sensor. With such a means, an apparatus is controlled by detecting the polarization current produced as a result of the thermal change when heat is transferred between a pyroelectric vapor sensor 4 and vapor 6 generated from food 5. (An example such as disclosed in Japanese Laid-Open Patent Publication No. 62-37624).
However, using a humidity sensor such as described above has had the problem that since the detection sensitivity of the humidity sensor drops because of adherence of gas and oil from food during the cooking of the food, the deposits on the humidity sensor have to be vaporized for each cooking using a refresh heat-treat heater or the like, thus requiring extra electricity and additional costs.
On the other hand, in the case of using a pyroelectric vapor sensor instead of the humidity sensor, if the construction is such that the pyroelectric vapor sensor is installed in an exhaust flue or in a vapor vent, the pyroelectric vapor sensor is heated to a considerably high temperature because it is directly subjected to hot vapor and also because the temperature of the surrounding oven, cabinet, etc., rises. Since the pyroelectric vapor sensor provides an output according to the temperature difference .DELTA.T between the hot vapor and the sensing element, the above construction has had the problem that when the temperature of the pyroelectric vapor sensor rises, the .DELTA.T becomes smaller, causing a drop in the sensor output. In other words, when an apparatus is controlled according to the output from the pyroelectric vapor sensor, the sensor output drops as cooking is repeated and as the temperature of the pyroelectric vapor sensor rises, and therefore, a longer detection time is needed even when cooking food of the same kind, causing a variation in the cooking results unless corrected by using a device for temperature compensation or by including software for adjustment. This has been the problem with the above construction yet to be solved.